Process for retorting carbonaceous material

ABSTRACT

AN IMPROVED PROCESS FOR RETORTING CARBONACEOUS MATERIAL, SUCH AS OIK SHALE, WHERE THE HET OF PYROLYSIS IS SUPPLIED BY MIXING HOT SPENT SHALE ASH WITH RAW SHALE FEED SHALE PARTICLWS LOSE THEIR STRENGTH PROGRESSIVELY ABOVE ABOUT 500*F. SO CRUSHING OF THE FEED TO MINUM 1/8 INCH SIZE DOES NOT TAKE PLACE UNTIL AFTER MIXING OR RETORTING. COLD SHALE FEED FINES ARE ADDED TO THE MIXED HOT SHALE ASH AND LARGER SHALE FEED BEFORE RETORTING.

Aug. 3, 1971 R. 'r. ELLINGTON, JR 3,597,347

PROCESS FOR RETORTING CARBONACEOUS MATERIAL Filed Dec. 6, 1968 TOPRODUCT 8 I6 RECOVERY l7 km WASTE l2 4-- AIR INVEN'IFOR REX T.ELLINGTON,JR.

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ATI'UHNEYH United States Patent 3,597,347 PROCESS FOR RETORTINGCARBONACEOUS MATERIAL Rex. T. Ellington, Jr., Tulsa, Okla, assiguor toThe Oil Shale Corporation, New York, NX. Filed Dec. 6, 1968, Ser. No.781,769 Int. Cl. Cb 53/06 US. Cl. 208-11 9 Claims ABSTRACT OF THEDISCLOSURE An improved process for retorting carbonaceous material, suchas oil shale, where the heat of pyrolysis is supplied by mixing hotspent shale ash with raw shale feed. Shale particles lose their strengthprogressively above about 500 P. so crushing of the feed to minum /3inch size does not take place until after mixing or retorting. Coldshale feed fines are added to the mixed hot shale ash and larger shalefeed before retorting.

This invention relates to the removal of volatile material from solidcarbonaceous material. More particularly, this invention relates to animproved process for the recovery of volatile material, such ascombustible gases, liquid motor fuels, and various grades of oil, fromsolid carbonaceous material, such as oil shale, tar sand, coal, ligniteand the like.

Many techniques have been employed for thebeneficiation of solidcarbonaceous material. For example, oil shale has been retorted inbatch-type tfixed bed operations, rotating drums, chain grate kilns,moving bed retorts and fluidized beds.

One of the processes of recent interest is the sandcracking process. Inoperation, spent shale ash preheated to about 1200 F. is mixed with coldraw shale feed that has been previously crushed to minus inch size. Thespent shale ash thus provides the heat of pyrolysis. After mixing, theshale ash and feed are discharged into a retorting vessel. The size ofthe vessel and the rate of withdrawal of spent shale ash are in suchrelationship that the shale feed has adequate time to absorb heat fromthe shale ash and to be fully retorted before it is discharged from theretort vessel. Air is introduced into the solid efiiuent discharged fromthe retorting vessel and the air-entrained efiluent is passed into alift-tube combustor where the carbon content of the spent shale isburned off to heat the air and the shale ash to the desired temperature.At the top of the lift pipe, part of the entrained shale ash is knockedout and dropped in the retention bin to provide heat for retorting. Theremainder is carried off with the hot combustion products, through awaste heat boiler and/ or any other heat recovery means and then througha cyclone where the ash is separated from the cooled combustion productsand sent to disposal. The gaseous retort products are withdrawn from thetop of the retort vessel and transferred to a hot-dust separator wherethe entrapped waste dust is removed. The thuspurified gaseous retortproducts are then conventionally treated to remove oil and otherproducts.

While this process, as outlined above, offers oil yields of at least 90%Fischer Assay, it also presents problems. The raw oil shale feed must becrushed from a size of 1 inch or more to the minum A2. inch size to giveoptimum operation of the lift-tube combustor. Also. there is thepossibility that the burned off shale ash will absorb shale oil vaporsin the retorting drum and thus carry part of the yield from new shaleout to the combustor, thus reducing the yield in the recovery system.

It is an object of this invention to provide an improved process forretorting carbonaceous materials, particularly oil shale, where the heatof pyrolysis is supplied by hot spent shale ash wherein the priorcrushing of the raw shale feed is made easier or some stages of crushingeliminated. It is a further object of this invention to provide animproved process for retorting carbonaceous materials, particularly oilshale, wherein the heat of pyrolysis is supplied by mixing the feed witha heatcarrying solid and the retort yield is maximized by controllingthe retort atmosphere and other process variables.

These objects and other advantages are achieved by mixing shale ash of atemperature of about l000 to 1500 F. preferably 1200 to 1400 F. withcold raw oil shale feed fines and larger feed of a size of about minus1.5 inch to minus 1 inch down to /8 inch, the larger feed preferablybeing preheated to about 500 to 550 F., transferring the mix to a retortvessel wherein the atmosphere is maintained non-combustion supporting(an atmosphere of natural gas or processed retort gas containing 10 vol.percent CO is preferred), retorting otf volatile material at a preferredretort temperature of about 800 to 950 R, such as oil, with the heat ofpyrolysis supplied by the hot spent shale ash, crushing the shalemixture at temperature above about 500 F. to essentially minus inchsize, preferably minus inch size, passing the spent shale through alift-tube combustor by the addition of air where the carbon content ofthe spent shale is burned off to heat the air and shale ash to thedesired temperatures, and recycling part of the heated spent shale backto the mixer for mixing with raw feed oil shale.

It has been found that oil shale commences to lose crushing strengthabove about 500 F. and is very friable by the time it reaches retorttemperature and is retorted. As a consequence, crushing of the oil shaleabove about 500 F. is much easier and requires less extensive crushingapparatus to achieve the fineness normally sought in the low tempearturecrushing. Retorting for the oil can be done with the large pieces nearlyas easily as with the finer particles normally used. However, finerparticles are desirable for flow through the lift-tube combustor underthe action of air. The crusher can thus be placed in the processanywhere the shale is at a temperature of over 500 F. and before thelift-tube combustor. It may thus be placed at the outlet of the mixer,or, if residence time in the mixer is not sufficient to raise the rawshale temperature to above 500 F. and larger particles in the retortvessel do not affect yield, at the outlet of the retort vessel.

The figure is a schematic diagram of the process of my invention.

Referring to the figure, raw shale feed 1 of a size of about minus 1.5inch to minus 1 inch is fed into the raw shale preheater 2 where thefeed 1 is preheated to a temperature range of about 500 to 550 F. Thepreheater is heated by heat taken from the ash and flue gas taken fromthe retort vessel as described below. The preheated raw shale feed 3 isthen transferred to a mixer 4, Which can be any conventional mixingapparatus such as a screw mixer, where it is mixed with hot shale ash 5from the retention drum 6, described below, and fine-size, i.e., minus 4inch, raw shale feed 7. The fine-size raw shale feed 7 is preferablyseparated from the larger raw shale feed 1 before the latter ispreheated. The mixed shales 8 are then transferred to the retortingvessel 9. If the mixed shales 8 are discharged at a. temperature of 500F. or higher, a crusher 10 can be used between the mixer 4 and retortvessel 9 to crush the shale pieces to a size sufiicient to betransferred by air to the retention drum 6, i.e., essentially minus Ainch size, preferably minus inch size. If the discharge temperature atthe mixer 4 is not 5 00 F. or above or if it is desired to omit 3 anyfurther fine-size pieces that may carry away the oil vapor, the crushermay be inserted intermediate the discharge side of the retort vessel 9and the liftpipe 11, as indicated in the figure at 12.

The feed shale is retorted in retort vessel 9 with the heat of pyrolysissupplied by the hot shale ash 5. The retorting is carried out at atemperature range of about 500 to 1500 F., preferably 800 to 950 F. Thecharge of mixed sh ales 8 is preferably maintained during retorting in anon-combustion supporting atmosphere as taught in copending applicationSerial Number 781,901 filed of even date herewith. The atmosphere may bepure natural gas or a gas of similar composition but optimum results areachieved using an atmosphere of natural gas containing up to 20 volumepercent carbon dioxide, preferably 10 volume percent. Processed andrecycled retort gas can also be employed as the atmosphere. Thissurrounding atmosphere is injected into the retort vessel 9 at inlet 13.Compositional control can be achieved through conventional means such asan on-line chromatograph (not shown) and gas mixing. The gaseousefiluent 14 from the reactor vessel containing the retorted oil is takenoff the top of the retort vessel 9 and transferred to a hot dustseparator 15 through conventional piping. The dust-removed gas 16 istransferred to a conventional product recovery system 17 (not shown).The dust 18 removed in the separator is disposed of.

If extra insurance is needed against condensation in transfer piping orhot cyclones used to remove shale ash or shale dust from the retortvapor, extra gas of the same composition as surrounding the particles orrecycled processed retort gas and preferably preheated can be fed abovethe bed in the retort vessel 9 as indicated at 31 to lower the dew pointof the vapor stream leaving the retort.

The solid oil-depleted shale mixture 19 is removed from the retortvessel 9, passed through the optional crusher 12, as explained above,and is transferred into the lift-pipe combustor 11 by the injection ofair 20. As the solid-air mixture 21 passes up the lift-pipe combustor11, the carbon in the oil-depleted shale is burned off, raising thetemperature of both the shale and the air. At the top of the lift-pipe11 is a retention drum 6 into which the combusted shale ash istransferred. Part of this hot shale ash 22 is recycled into the mixer 4as explained above for heat transfer to the raw shale feeds 3 and 7. Thebalance of the hot shale as 22 and the flue gas combustion products fromlift pipe 11 are transferred into the heat exchanger 23, such as a wasteheat boiler. The cooled ash-gas mixture 24 is then further transferredto cyclone 25 where the shale ash and the flue gas are separated. Theflue gas 26 is then transferred into raw shale preheater 2 for direct orindirect heat exchange with the large-size raw shale feed 1. After thisexchange, the flue gas is vented into a stack as generally indicated at27. The shale ash 28 from cyclone 25 is transferred to shale ash cooler29 from whence it is disposed of as generally indicated at 30.

In another form of the invention the non-combustion supportingatmosphere 13 is used with special advantage. When all the material isfinely crushed (as to minus Ms inch) or the crusher 10 is inserted afterthe mixing vessel 4, the rate of injection can be controlled so that thebed in the retort vessel 9 is swept at a low rate to educt retortingproducts and obtain yield improvement. Injection can be controlled at ahigher rate to expand the bed and reduce the residence time of theretorting products in vessel 9, or at still higher rates to fluidize theupper part or all of the bed to minimize residence time of retortingproducts in the vessel. Such injection also serves to achieve the dewpoint reduction mentioned for over-bed injection above.

The following example further illustrates the invention.

4 EXAMPLE Raw shale feed of minus 1.5 in. size and at a temperature ofabout 60 F. is fed to a raw shale preheater where it is preheated to atemperature of about 520 F. The preheated raw shale is transferred to amixing vessel where it is mixed with hot shale ash at a temperature ofabout 1250" F. After one to three minutes residence time, the mixedshale ash and feed are discharged into a retort vessel maintained underan atmosphere of processed retort gas containing at least CH Shale oilis retorted from the feed with the heat of pyrolysis being suppliedbythe hot shale ash. After three to ten minutes residence time, the shaleash and shale coke at equal temperatures of about 875 F. are dischargedinto a crusher which crushes the mix to essentially minus A3 inch size.The crushed particles at a temperature of about 900 F. are transferredinto a lift-tube combustor by the injection of air. The carbon in theshale coke is burned off in the combustor. At the top of the lift-tubecombustor, the shale ash is transferred to a retention drum at atemperature of about 1250 F. Part of this shale ash is recycled back tothe mixing vessel for retorting. Part is transferred to a heat-exchangerunit where steam can be generated by heat exchange with the hot shaleash. The shale ash is then transferred to a cyclone where the shale ashand flue gas are separated. The hot flue gas is then transferred toftheraw shale preheater where it preheats the raw shale feed by direct orindirect heat exchange. The shale ash is transferred to a spent shaleash cooler from whence it is disposed of.

Table I shows the flow rates of materials in the example.

' TABLE I Stream Flow rate In: (lbs/hr.) Raw shale feed 916,667Fluidizing gas 62,861 Combustion air 355,347

Total 1,334,875

Out: '4 Retort vessel eflluent vapors 231,318 Spent shale ash todisposal 690,069 Flue gas 413,488

Total 1,334,875

Internal:

Preheated raw shale 916,667 Raw shale/ spent shale ash mixture (retortfeed) 2,223,741 Retort vessel effluent solids 2,055,284 Crusher product2,055,284 Combustion lift tube eflluent 2,410,631 Spent shale ash toretort 1,307,074 Flue gas plus spent shale ash 1,103,557 Flue gas to rawshale preheat 413,488 Flue gas to stack 413,488

What I claim is:

1. A process for the recovery of volatile material from solidcarbonaceous material wherein raw feed of the solid carbonaceousmaterial is mixed with hot ash of processed carbonaceous material, theraw feed-hot ash mixture is transferred to a retort vessel, the volatilematerial being retorted from the raw feed in the retort vessel with theheat of pyrolysis being supplied by the heat of the hot ash, theresulting spent mixture then being discharged from the retort vessel,mixed with air and transferred to a lift-tube combustor wherein at leastpart of the carbon of the spent mixture is burned off to form hot ashand flue gases, the hot ash at the end of the lift-tube combustor beingtransferred to a retention bin and thereafter part of the hot ash isthen mixed with raw feed to provide the heat of pyrolysis and thevolatile material; one of said mixtures of the group of raw feed-hot ashmixture and spent mixture being crushed to a smaller particle size at atemperature above 500 F. prior to transference of the spent mixture tothe lift-tube combustor.

2. The process of claim 1 wherein the solid carbonaceous material is oilshape and the voltile material contains oil.

3. The process of claim 1 wherein the raw feed-hot ash mixture iscrushed after mixing and before entering the retort vessel.

4. The process of claim 1 wherein the spent mixture is crushed afterbeing discharged from the retort vessel and before entering thelift-tube combustor.

5. The process of claim 3 wherein the raw feed of the raw feed-hot ashmixture before crushing consists essentially of particles of minus 1.5inch to about /8 inch size.

6. The process of claim 5 wherein the raw feed of the raw feed-hot ashmixture after crushing consists essentially of particles of minus /1inch size.

7. The process of claim 5 wherein the raw feed of the raw feed-hot ashmixture after crushing consists essentially of particles of minus inchsize.

8. The process of claim 2 wherein a non-combustion gas is present in theretort vessel and is one of the group consisting of natural gas,processed recycled retort gas, a gas of similar composition to naturalgas, and natural gas or processed recycled retort gas containing up toabout 20 volume percent carbon dioxide.

9. The process of claim 8 wherein the non-combustion supporting gas isnatural gas or processed recycled retort gas containing about 10 volumepercent carbon dioxide.

References Cited UNITED STATES PATENTS 2 656,308 10/1953 Pettyjohn 201-73,167,494 1/1965 Crawford 208-11 3,346,481 10/1967 Johnsen 208113,361,644 1/1968 Deering 208-11 CURTIS R. DAVIS, Primary Examiner U.S.c1. X.R. 201-7, 12, 20

